Kubernetes ConfigMap to write Node details to file - kubernetes

Question

How can I use ConfigMap to write cluster node information to a JSON file?
The below gives me Node information :
kubectl get nodes -o jsonpath='{.items[*].status.addresses[?(#.type=="Hostname")].address}'
How can I use Configmap to write the above output to a text file?

Answer 1

You can save the output of command in any file.
Then use the file or data inside file to create configmap.
After creating the configmap you can mount it as a file in your deployment/pod.
For example:
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
labels:
app: appname
name: appname
namespace: development
spec:
selector:
matchLabels:
app: appname
tier: sometier
template:
metadata:
creationTimestamp: null
labels:
app: appname
tier: sometier
spec:
containers:
- env:
- name: NODE_ENV
value: development
- name: PORT
value: "3000"
- name: SOME_VAR
value: xxx
image: someimage
imagePullPolicy: Always
name: appname
volumeMounts:
- name: your-volume-name
mountPath: "your/path/to/store/the/file"
readOnly: true
volumes:
- name: your-volume-name
configMap:
name: your-configmap-name
items:
- key: your-filename-inside-pod
path: your-filename-inside-pod
I added the following configuration in deployment:
volumeMounts:
- name: your-volume-name
mountPath: "your/path/to/store/the/file"
readOnly: true
volumes:
- name: your-volume-name
configMap:
name: your-configmap-name
items:
- key: your-filename-inside-pod
path: your-filename-inside-pod
To create ConfigMap from file:
kubectl create configmap your-configmap-name --from-file=your-file-path
Or just create ConfigMap with the output of your command:
apiVersion: v1
kind: ConfigMap
metadata:
name: your-configmap-name
namespace: your-namespace
data:
your-filename-inside-pod: |
output of command

Answer 2

At first save output of kubect get nodes command into JSON file:
$ exampleCommand > node-info.json
Then create proper ConfigMap.
Here is an example:
apiVersion: v1
kind: ConfigMap
metadata:
name: example-config
data:
node-info.json: |
{
"array": [
1,
2
],
"boolean": true,
"number": 123,
"object": {
"a": "egg",
"b": "egg1"
},
"string": "Welcome"
}
Then remember to add following lines below specification section in pod configuration file:
env:
- name: NODE_CONFIG_JSON
valueFrom:
configMapKeyRef:
name: example-config
key: node-info.json
You can also use PodPresent.
PodPreset is an object that enable to inject information egg. environment variables into pods during creation time.
Look at the example below:
apiVersion: settings.k8s.io/v1alpha1
kind: PodPreset
metadata:
name: example
spec:
selector:
matchLabels:
app: your-pod
env:
- name: DB_PORT
value: "6379"
envFrom:
- configMapRef:
name: etcd-env-config
key: node-info.json
but remember that you have to also add:
env:
- name: NODE_CONFIG_JSON
valueFrom:
configMapKeyRef:
name: example-config
key: node-info.json
section to your pod definition proper to your PodPresent and ConfigMap configuration.
More information you can find here: podpresent, pod-present-configuration.